How oil might affect a hurricane

There's no major changes to the forecast for the Gulf of Mexico oil spill. As I discussed in yesterday's post, on Sunday, the winds will begin increasing and shifting to the southeast. The latest run of the GFS model shows that this will be a week-long period of southeast winds, with wind speeds at times reaching 20 - 25 knots. These winds will threaten to bring oil to a large portion of the Louisiana coast, including regions of the central Louisiana coast west of the mouth of the Mississippi River. The Mississippi and Alabama coasts will also be at risk next week, but the risk to the Florida Panhandle is lower. Yesterday's post also has the long-range outlook for oil to get into the Loop Current and spread to the Florida Keys and beyond.

What will oil in the Gulf of Mexico do to a hurricane?With hurricane season fast approaching and the oil spill in the Gulf of Mexico likely to still be around once hurricane season starts in June, we need to ask, how will oil affect any hurricanes that might traverse over the spill? And how might a hurricane's wind and storm surge affect the spill? Let's consider the first of those questions today.

From the time of the ancient Greeks to the days of the wooden ships and iron men, mariners dumped barrels of oil onto raging seas to calm them during critical moments of violent storms (Wyckoff, 1886.) Oil does indeed calm wind-driven waves, thanks to the reduction in surface tension of the water that oil causes. Ripples with a wavelength shorter than 17 mm are affected by surface tension, and these ripples then cause a feedback that reduces the height of larger waves with longer wavelengths (Scott, 1986.) The reduction of surface tension also impacts the flow of air above the water, and reduces the amount of sea spray thrown into the air, both of which could affect the wind speed. Oil also damps waves by forming a thick, viscous film at the top of the water that resists water motion (Scott, 1999.) Oil also helps calm raging seas by switching off of the wind energy input needed by the wave to break. This occurs because the surface film of oil prevents the generation of ripples on the exposed crests of the waves, and this smoother surface makes the wind less able to grab onto the wave and force it to break.

So, what would happen to a hurricane that encounters a large region of oily waters? A 2005 paper by Barenblatt et al. theorize that spray droplets hurled into the air by a hurricane's violent winds form a layer intermediate between air and sea made up of a cloud of droplets that can be viewed as a "third fluid". The large droplets in the air suppress turbulence in this "third fluid", decrease the frictional drag over the ocean surface, and accelerate the winds. According to this theory of turbulence, oil dumped on the surface of the ocean would reduce the formation of wind-whipped spray droplets, potentially calming the winds. The authors propose spraying oil on the surface of the ocean to reduce the winds of a hurricane. However, the turbulence theory championed by Barenblatt et al. has been challenged by other scientists. In a 2005 interview with Newscientist magazine, turbulence expect Julian Hunt at University College London, UK, remarks, "I am very doubtful about this approach." Hunt studies turbulence both theoretically and in the laboratory, and believes that the high wind speeds in a hurricane are not caused by sea spray. In an article he wrote for the Journal of Fluid Dynamics, Hunt suggests that variations in the turbulence between different regions of the hurricane cause sharp jumps in wind speed, which are responsible for the hurricane's strongest winds.

Oil reduces evaporationHurricanes are sustained by the heat liberated when water vapor that has evaporated from warm ocean waters condenses into rain. If one can reduce the amount of water evaporating from the ocean, a decrease in the hurricane's strength will result. Oil on the surface of the ocean will act to limit evaporation, and could potentially decrease the strength of a hurricane. However, if the oil is mixed away from the surface by the strong winds of a hurricane, the oil will have a very limited ability to reduce evaporation. According to a 2005 article in Popular Science magazine, Dr. Kerry Emanuel of MIT performed some tests in 2002 to see if oil on the surface of water could significantly reduce evaporation into a hurricane. He found that the slick quickly dissipated under high wind conditions that generated rough seas.

Figure 1. A comparison of the size of 2008's Hurricane Gustav with the size of the Gulf oil spill. The spill is only about 60 miles in diameter, while a hurricane like Gustav is typically 400+ miles in diameter.

ConclusionA tropical cyclone in its formative stage--as either a tropical depression or a tropical storm with 40 mph winds--might be adversely affected if it encountered the Gulf of Mexico oil slick, due to the reduction of evaporation into the storm. However, a full-fledged hurricane would mix the oil into the ocean to such a degree that the storm would probably not see any significant reduction in evaporation. It remains unknown how the reduction of sea spray by oil might affect a hurricane. If the oil slick expands to a much larger size, there might be a significant reduction in strength of the hurricane, if theory of how a reduction of sea spray will decrease a hurricane's winds is correct. However, the oil slick is currently Delaware-sized, while a hurricane tends to be Texas-sized, and I doubt that the oil slick at its current size is large enough to have a significant impact on a hurricane's intensity. The slick is about 60 miles across, and it would take a hurricane about four hours to traverse the spill at a typical hurricane forward speed of 15 mph. Furthermore, the slick is within 50 miles land, and interactions with land will dominate the behavior of a hurricane that gets that close to the coast. Unfortunately, there is a decent chance that we'll get a real-world opportunity to see what will happen. June tropical storms tend to form in the Gulf of Mexico, and we've been averaging one June storm every two years since 1995. This year, the odds of a June Gulf of Mexico storm are probably a little lower than usual, shear from our lingering El Niño may bring wind shear levels a bit above average. I expect there is a 20% chance that we'll see a June tropical storm in the Gulf of Mexico that would interact with the oil spill.

First tropical wave of the season leaves the coast of AfricaYesterday, the National Hurricane Center noted the first tropical wave of the year coming off the coast of Africa in their Tropical Weather Discussion. The first half of May is the typical time when the first tropical wave comes off the coast of Africa. The wave is currently positioned in the far eastern Atlantic near 5N 45W, and I don't expect it to develop, since it is too close to the Equator to leverage the Earth's spin to gain the rotation needed. The wave has quickly been joined by two new ones today, located at 15W and 36W off the African coast. Tropical waves serve as the seed that form most Atlantic and Eastern Pacific hurricanes.

Portlight delivers major aid shipment to HaitiPortlight continues to focus its energy and funds on the situation in Haiti, where the rainy season is fast approaching the needs for shelter, medical supplies, food and water remain urgent. Their latest effort was a shipment of several thousand pounds of Durable Medical Equipment and 30,000 pounds of rice that arrived this week via the schooner Halie and Mathew.

Portlight.org is also preparing to respond the the Gulf Coast oil spill by deploying one of more mobile kitchens to feed the hundreds of volunteers likely to flood the coast when the oil finally comes ashore. Please visit the Portlight.org web site or the Portlight blog to learn more and to donate to Portlight's efforts in Haiti and the Gulf Coast.

Figure 2. Relief supplies from the schooner Halie and Mathew sitting at the Portlight Haiti warehouse, ready for distribution.

Next PostI'm on my way to Tucson today for the American Meteorological Society's 29th Conference on Hurricanes and Tropical Meteorology, which will be held in Tucson next week. My next post will probably be on Monday night, when I plan to discuss the record SSTs observed last month in the tropical Atlantic. I'm excited to be catching up on and blogging about all the latest advancements in hurricane research!

Hi Jeff,For a trip to the Bahamas July 2-5th should we worry about oil or hurricane activity? My research has led me to believe oil will not be a factor but I'm having a hard time with predicting any tropical weather disruptions. Can you help?

I would think that a worst case scenario might be if the oil was a foot or so subsurface. It would not impede evapoation as much and may have a warming effect by absorbing sun heat. Add to that the wave dampening effects and I see a potential for pretty high wind speeds. I've been out at the beginning of gales (I was Coast Guard) and watched how the wind would be at a high speed before the waves built, then it would usually slow down a bit at the surface. Seemed that way to me, anyway.Wonder if the salinity of the water gets affected ? That, too, would get odd.

That's wonderful(or should I say wunderful) news Storm W.! Welcome back! P.S.- What's the weather going to be like next week for your area...we're going to be in your neck of the woods for vacation; fishing on Honeymoon Island.

A very nasty spring day is underway up here in Alaska. A 980mb low with deep tropical moisture connections moving up from the south over the Alaska Peninsula is creating a strong pressure gradient between itself and a high pressure ridge over western Canada. We're having a rather blustery day here with 30mph sustained winds out of the southeast with gusts exceeding 45mph, accompanied by moderate rainfall. This is pretty potent for a storm this late in the year, even by Alaskan standards.

Dr. Masters intends to put me on as a featured blogger this season...soon. I wanted to take the opportunity to establish some ground rules.

Per Dr. Masters email: Of course, we would expect you to conduct yourself in a professional manner, as if you were a representative of our company, in all of your posts, comments, and wumail exchanges.

When visiting my site this season, it will be appreciated that posts be made in good taste, bearing in mind Jeff's statement. I don't mind if you disagree with me on my forecasts or views. Just make sure you're civil, and professional. Anything less, and you will be banned from my blog...permanently!

Dr. Masters intends to put me on as a featured blogger this season...soon. I wanted to take the opportunity to establish some ground rules.

Per Dr. Masters email: Of course, we would expect you to conduct yourself in a professional manner, as if you were a representative of our company, in all of your posts, comments, and wumail exchanges.

When visiting my site this season, it will be appreciated that posts be made in good taste, bearing in mind Jeff's statement. I don't mind if you disagree with me on my forecasts or views. Just make sure you're civil, and professional. Anything less, and you will be banned from my blog...permanently!

Dr. Masters intends to put me on as a featured blogger this season...soon. I wanted to take the opportunity to establish some ground rules.

Per Dr. Masters email: Of course, we would expect you to conduct yourself in a professional manner, as if you were a representative of our company, in all of your posts, comments, and wumail exchanges.

When visiting my site this season, it will be appreciated that posts be made in good taste, bearing in mind Jeff's statement. I don't mind if you disagree with me on my forecasts or views. Just make sure you're civil, and professional. Anything less, and you will be banned from my blog...permanently!

Not much going on across the Atlantic due to the downward pulse of the MJO. Lots of dry sinking air dominates the region providing fair conditions Despite this downward pulse, the ITCZ is convective. Most models agree on an upward pulse and increase in moisture later this month.

Much of the dry air is above 850 mb so areas across the region may get an isolated shower or two. Thunderstorm will occur if the enough heat is added to the low levels to keep convective currents going upwards.

Split the lawsuits they're going to lose 3 ways. Split the reimbursement of lost wages for those who now can't work, 3 ways.

It's going to destroy this areas most profitable income.

What a total disaster.

The whole thing stinks as far as Halliburton is concerned.....As you know many prominent US politicians and defence and intelligence officials are on the company "take" as board directors, shareholders, and consultants which is how they are involved in so many government "no bid" contracts and provide services worldwide......They just need to pony up on this one and tighten their belts like everyone else..........Sorry folks; end of political diatribe from me.....Praying now for the vitims and families of the tornadoes...

Quoting weathermanwannabe:Good Morning........Just heard on NPR that Halliburton, Transocean, and BP are pointing the finger at each other for the accident in Senate Hearings starting today........Easy solution.......Split the cleanup costs three ways.

Split the lawsuits they're going to lose 3 ways. Split the reimbursement of lost wages for those who now can't work, 3 ways.

Also note the incredibly cosmic connection between Halliburton and the "Gulf"; major contractor for the "Gulf" war; cleanup contracts after Katrina in the "Gulf", and now, the "Gulf" oil spill.......Looks like they have a lock on the "Gulf" if you ask me....... :)

Good Morning........Just heard on NPR that Halliburton, Transocean, and BP are pointing the finger at each other for the accident in Senate Hearings starting today........Easy solution.......Split the cleanup costs three ways.